Hydrogen fueled vehicles, sometimes referred to as the Freedom Car are receiving considerable interest as part of a plan to reduce the reliance on foreign oil and reduce pollution. There are several current designs of hydrogen cars, with one example being a fuel cell powered vehicle commonly called an FCV. In the FCV, hydrogen is supplied to a fuel cell which produces electricity, which is used to power electric motors that propel the vehicle. Another type of hydrogen car is based upon a hydrogen internal combustion engine (HICE). In both designs, hydrogen is the fuel source with water being generated as the combustion byproduct.
A central issue with respect to both types of hydrogen vehicles, i.e., the FCV and HICE vehicles, is one of fuel supply. Not only is there a large infrastructure required for hydrogen dispensation, if one considers all the service stations, production and distribution equipment that are required, but there are issues with respect to fuel handling and use of the fuel on the vehicle itself. Before there can be a progression to dedicated fuel cell propulsion systems and hydrogen internal combustion engines, one must foresee a fuel infrastructure.
Two sources of hydrogen for use in hydrogen cars include the reforming of natural gas (fossil fuels) or from water using electrolysis. Once hydrogen gas is generated it must be stored for subsequent filling of cars or converted into a liquid fuel. Storage of hydrogen gas requires compression and transfer to a cylinder storage vessel. And, if the gaseous hydrogen is stored on the vehicle, such storage cylinders are expensive and they can represent a possible safety hazard in the case of an accident. Alternatively, hydrogen can be stored under low pressure in metal hydride canisters, but, at present, hydride canisters are a lot more expensive than cylinders.
Liquid methanol and other alcohols have been touted as particularly attractive hydrogen sources because they can be catalytically converted over a catalyst allowing pure hydrogen to be released on demand. On site conversion of liquid fuels to gaseous hydrogen overcomes the disadvantages of gaseous storage. Further, fuels such as methanol, and other alcohols are not overly expensive and there is an infrastructure in place today that allows for handling of liquid fuels. Although methanol and alcohols are suitable as a fuel source, they are consumed in the combustion process. In addition, the byproducts of such catalytic conversion, carbon dioxide and water, cannot easily be converted back to a hydrogen source.
Representative patents illustrating hydrogen storage and use are as follows:
Hydrogen Generation by Methanol Autothermal Reforming In Microchannel Reactors, Chen, G., et al, American Institute of Chemical Engineers, Spring Meeting, Mar. 30-Apr. 3, 2003 pages 1939-1943 disclose the use of a microchannel reactor as a means for conducting the endothermic steam-reforming reaction and exothermic partial oxidation reaction. Both reactions are carried out in the gas phase.
Scherer, G. W. et al, Int. J. Hydrogen Energy, 1999, 24, 1157 disclose the possibility of storing and transporting hydrogen for energy storage via the catalytic gas phase hydrogenation and the gas phase, high temperature, dehydrogenation of common aromatic molecules, e.g., benzene and toluene.
US 2004/0199039 discloses a method for the gas phase dehydrogenation of hydrocarbons in narrow reaction chambers and integrated reactors. Examples of hydrocarbons for dehydrogenation include propane and isobutane to propylene and isobutene, respectively. Reported in the publication are articles by Jones, et al, and Besser, et al, who describe the gaseous dehydrogenation of cyclohexane in a microreactor. Jones, et al employ a reported feed pressure of 150 kPa and an exit pressure of 1 Pa.
U.S. Pat. No. 6,802,875 discloses a hydrogen supply system for a fuel cell which includes a fuel chamber for storing a fuel such as isopropyl alcohol, methanol, benzene, methylcyclohexane, and cyclohexane, a catalytic dehydrogenation reactor, a gas-liquid separation device wherein byproduct is liquefied and separated from the gaseous dehydrogenation reaction product, and a recovery chamber for the hydrogen and dehydrogenated byproduct.